Nickel requires hypoxia-inducible factor-1α, not redox signaling, to induce plasminogen activator inhibitor-1

Abstract

Human epidemiological and animal studies have associated inhalation of nickel dusts with an increased incidence of pulmonary fibrosis. At the cellular level, particulate nickel subsulfide inhibits fibrinolysis by transcriptionally inducing expression of plasminogen activator inhibitor (PAI)-1, an inhibitor of the urokinase-type plasminogen activator. Because nickel is known to mimic hypoxia, the present study examined whether nickel transcriptionally activates PAI-1 through the hypoxia-inducible factor (HIF)-1α signaling pathway. The involvement of the NADPH oxidase complex, reactive oxygen species, and kinases in mediating nickel-induced HIF-1α signaling was also investigated. Addition of nickel to BEAS-2B human airway epithelial cells increased HIF-1α protein levels and elevated PAI-1 mRNA levels. Pretreatment of cells with the extracellular signal-regulated kinase inhibitor U-0126 partially blocked HIF-1α protein and PAI-1 mRNA levels induced by nickel, whereas antioxidants and NADPH oxidase inhibitors had no effect. Pretreating cells with antisense, but not sense, oligonucleotides to HIF-1α mRNA abolished nickel-stimulated increases in PAI-1 mRNA. These data indicate that signaling through extracellular signal-regulated kinase and HIF-1α is required for nickel-induced transcriptional activation of PAI-1.